Method of manufacturing black-heart malleable cast iron from white cast iron



Patented Nov. 27, 1928.

UNITED STATES PATENT OFFICE. 4

TABTO KIKUTA, OF TOBATA CITY, F UKUOKA KEN, JAPAN, ASSIGNOR TO TOBATAIMONO KABUSHIKI KAISHA, F TOBATA CITY, IUKUOKA KEN, JAPAN, A COB-roRA'rroN or JAPAN.

METHOD OF MANUFACTURING BLACK-HEART MALLEABLE CAST IRON FROM WHITE'CAS'J. IRON. I v

No' Drawing.

I exposing same in the open air. The object of the invention is to sparepacking material which has hitherto been necessary for the annealingprocess and also to shorten the anneal-- ing time. Moreover, thisinvention does not only produce castings of a uniform and superiorquality, but also entirely prevents the black heart malleable cast ironfrom becoming brittle under heat treatment like hot alvanizing orsherardizing as when the or inary 2 process-of annealing is used andalso, the superior quality of=iron obtained by th1s invention willremain unaffected by a temperature below the freezing point of water.

To obtain black heart malleable cast iron '25 by annealing white castiron, it is common to fill an annealing pot with white cast irontogether with sand, a mixture of sand and iron oxides, air furnaceslag,or 'ash; charge an annealing furnace with same; and heat it, withcoal, coal gas, fuel oil or electric current at a temperature rangingfrom 850 C. to 920 C.

for 7 0 to 100 hours. Then the pot is allowed to a cool very slowly inthe furnace. It being possible by this method to maintain a hightemperatur'e for a considerable length of time, it is possible tocomplete the graphitization of free cementite., but since the eutectoidcement- 'to produced at Ar, transformation point is Eraphitized onlyduring the cooling period 40 of the furnace, the graphitization cannotbe completed by the ordinary method when the quantities of carbon,silicon, and other elements contained in white cast iron are little,

or the capacity of the furnace is small. As

I regards the quality of black heart malleable cast iron produced, theperfect graphitization of this eutectoid cementite, as well as that ofApplication filed September 29, 1926. Serial No. 13 8,575.

the above free cementite, is of vital importance.

In an annealing according to my invention, the packing materialindispensable in the method hitherto known can be dispensed with. Theproper temperature between 850 and 950. is kept up constantly for 15 to60 hours in order to graphitize free cementite. Then, the temperature islowered to between 730 and 650 C., and after the temperature ismaintained within this limit for 20 to 50 hours, the pot is taken out ofthe furnace and cooled in the open air. When a muflle furnace 15 used,the product is either taken out and cooled in the open air or quenchedin water. The temperatures and length of time to be thus constantlymaintained should be selected and properly kept within a given limitaccording to the chemical composition of the white cast iron.

Thus, accordingto my method it ispossible to prevent the imperfectgraphitization of entect'oid cementite due to the shortage of car'- bonor silicon or the excess of the other elements contained in white castiron such as manganese, sulphur and chromium which occurs in the methodhitherto known. Besides, it is possible to shorten the time required forheating andcooling the furnace, because I do not use the packingmaterial indispensable in the old method which adds tothe' slowness ofthe'cooling of a furnace due to its poor conductivity after the fire isextinguished, so that the time of one cycle of annealing can be reducedconsiderably, for example, by nearly 3 or days ina lO-ton furnace.Further, as

non-conductors of heat such as sand, iron oxide, slag, etc. areunnecessary, the operation is very much simplified, the annealingreduced, and the product obtained is of a superiorand more uniformuality.

The black heat malleab le cast iron manufactured by ordinary annealingmethods becomes very brittle as a rule, when subjected to a heattreatment such as hot galvanizing or sherardizing; that is to say, whenheatedat a ;temperature of 300 to 550 C. and then immersed in cold orboiling water. However, the product made according to my inventlonretains its original quality permanently, even if subjected to a violentheat treatment. In

fact, it may be heated to any temperature below Ar transformation pointand then directly quenched in cold or boiling water or exposed to atemperature below the freezmg point of the water.

To show a manner of carrying out the present invention in practice, Igive below ex-' amples of annealing process with the annealing furnacesheated by pulverlzed coal (1) and electricity (2) respectlvely.

Annealing furnaces used.

(1) Is charged with about 10 tons of the product.

(2) Is charged with about 600'kilograms of the product.

Method of charging.

Method of annealing.

In.(1), the furnace was heated at 900 C. for 40 hours to complete thefirst stage of aphitization (mainly of free cementite). or the secondstage of graphitization (chiefly of eutectoid cementite) a temperatureof 700 C. was' maintained for 40 hours. Soon after the fire wasextinguished, the pots were taken out of the furnace and cooled in theopen air as they are.

In (2), so as to carry out the first stage of graphitization the furnacewas heated at 920 C. for 28 hours. Then, to complete the second sta e ofgraphitization a temperature of 710 was maintained for 35 hours. Afterthat, the product was taken out of the furnace. Then a part of itwasquenched in cold water and the rest exposed in the open air to effectrapid cooling.

Result of annealing.

As a means of test, first a part of the product was broken and thefracture examined.

' Then, tensile and bending tests were conducted with tensile andbending test pieces made of the same melt, which has been annealed inthe same furnace withthe products, and it was found out that it had beenperfectly annealed, the fracture presenting a velvet-like grey color.

The following are the results ofthe tens1on and bending tests Tensiontest.

' Bend- Treetment after the comple- No. of Eloningtest tion of thesecond stage of test Tensile gatiou (inner graphitization. piece.strength in radius (kg./ (gauge 35mm.) mmJ) length= 50 mm) 995 A 36. 5016.0 180 Agegrliiollgdplptroducts in the an B 3160 16 5 180 as at: a Aircooled products taken out 996 B 36. 90 15. 5 180 of the pot. 8g 2 g g 52 Qu'enched in-the water, prod- 997 B 1 1 n .85 15.5 180 ucts aken outof the pot. 997 0 3a 18 m 0 180 The tension test pieces used in theabove test were inch in diameter, and thebending test pieces had asection of inch in thickness and inch in breadth.

Next, the black heart malleable cast iron manufactured by the annealingmethod of my invention and the malleable cast iron manufactured by anordinary process were subjected to a heat treatment similar to thoserequired for hot galvanizing or shera'rdizing; that is to say, heated ata temperature of 450 C. for 20 in the cold water. After being thoroughlycooled, the were subjected to an impact test, and the fo lowing resultswere obtained (the same result was obtained with boiling water insteadof cold water, and therefore, that result is omitted) l.

minutes; and then immersed Black heart malleable cast iron manufacturedby annealing according to the present invention. Black heart malleablecast iron 11191111180 Cooled in the Cooled in the Cooled in the li byair in a pot after air outside a cold water after ordmm anneal thecompletion not after the the completion l of the second completion of ofthe second stage of graphthe second stage stage of graphltlzation. ofgraphitization itizatlon.

Before After Before After Before After Before After the the the the thethe the the heat heat heat heat heat heat heat heat treattreattreattreattreat: treattreattreat ment. ment. ment. ment ment. meat. ment. meat.

For the above impact test, a Char y impact testing machme and thestandar notched bars were used and the meter-kilogram system was adoptedasunits.

From the above it will be seen that the black heart malleable cast ironmanufactured according tofthemethods of annealing of this inventionundergoes no change in the quality under a heat treatment such as isused for hot galvanizing or sherardizing.

Thev above is more] one example of the annealing done accord ing to thisinvention,

and although the temperature and the time of heating should receive dueconsideration according to the size of a furnace and the method ofheating it, etc., the essential point is to cool rapidly the productafter carrying out the complete graphitization of the combined carboncontained in the white cast iron in two stages.

I claim- 1. A method of manufacturing black heart malleable cast ironfrom white cast iron without using packing material which comprisesfirst maintaining the white cast iron at a temperature between 850 and950 C. for 15 to 60 hours, then cooling the iron to a temperaturebetween 730 and 650 0., and then maintaining the iron at the lattertemperature for to 50 hours.

2. A method of manufacturing black heart malleable cast iron from whitecast iron without usin packing material which comprises firstmaintaining the white cast iron at a temperature between 850 and 950 Cfor 15 to 60 hours, then cooling the iron to a temperature between 730and 650 C., then maintaining the iron at thelatter temperature for 20 to50 hours, and then removing iron from the furnace and cooling it rapntestimony whereof I have aflixed my signature.

v TARIO KIKUTA.

